Conventional glass sheet processing systems for heating and forming a glass sheet include a glass sheet heating furnace and adjacent forming apparatus. Typically, a roller conveyor including a plurality of conveyor rolls is used to support and convey the glass sheet through the heating furnace in a direction of glass sheet conveyance. At the end of the furnace is a topside support means for receiving the heated glass sheet from the roller conveyor. The topside support means supports the glass sheet by vacuum pressure from above. In a next step, a mold shuttleable under the topside support means receives the glass sheet for further processing.
Alternatively, an air floatation furnace has been used for heating glass sheets. In these furnaces, hot air is used to support the glass sheet in the furnace above a heating bed that slopes upwardly in the direction of glass sheet conveyance. The hot air acts like a frictionless air bearing and the glass sheet is guided and pushed by a conveyor having pusher bars that push the glass uphill through the furnace.
In order to use such an air floatation furnace with a topside support means, it becomes necessary to get the pusher bars out of the way before the glass sheet arrives at the topside support means. The reasons are twofold; so that the pusher bars do not interfere with locating devices, such as that disclosed in U.S. patent application Ser. No. 554,373 and also so that the shuttle is movable beneath the air support means for receiving the heated glass sheet for further processing.
Furthermore, it is necessary to slow down the speed at which the glass sheet is travelling in the direction of glass sheet conveyance in order to properly position the heated glass sheet on the topside support means for further processing. Slowing down the rate of speed of the conveyed glass sheet can only be accomplished by continuously regulating the speed of the pusher bars.